<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/vue/2.6.10/vue.js"></script>
</head>
<body>
    <div id="app">
        <p :class="{active:isActive}">hello world</p>
        <p :class='["one",flag?"two":""]'></p>
    </div>
    <script>
        var vm=new Vue({
            el:"#app",
            data() {
                return {
                    isActive:true,
                    flag:true
                }
            },
        })
    </script>
</body>
</html>